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Is it possible to design a helicopter with fixed rotor blades only (no blade angle/flap/pitch)?
I am not familiar with helicopter rotor design but I wonder if it is possible to build a working/flying helicopter with fixed rotors that cannot change the blade angle, flap, pitch or adjust blades otherwise?
I am curious whether the changes in rotation speed would suffice for controlling the aircraft. I guess the cheap RC helicopter models may use such simple design, but is it possible to scale that up to 1:1?
I mean propellers that are solid state and cannot be adjusted in any way except changing their rotation speed, like plastic props used in RC modelling. I do not mind if the whole helicopter design is a traditional main rotor + tail rotor or a coaxial rotor design.
I am interested in 1:1 scale size (at least the Mosquito personal helicopter size). Has anyone tried such simple design?
Also I consider electric propulsion where the RPM changes may be quicker that with internal combustion engines.

Not a helicopter in the traditional sense, but the Volocopter is essentially a multi-rotor drone with a seat or three for people.  It drives many fixed pitch blades with as many electric motors.  I want one.

I want a single rotor (or coaxial) design though.

Apart from the necessity of leading/lagging and flapping as explained in KorvinStarmasts answer, rotation speed is not the ideal way to control lift, at least not in a full size helicopter. The main rotor has far too much inertia to provide for the fast and suble changes that are necessary. So RPM is maintained (almost) constant, while lift is controlled by changing the blades' angle of attack collectively, or cyclicly to control pitch and roll. Yaw is controlled the same way by changing the pitch of the tail rotor blades.

Would you consider NOTAR-like solutions? That entirely drops the tail rotor.

Scaling laws are your enemy here.
Model helicopters can be controlled with changes in rotational speed, but for full-sized helicopters the energy needed to quickly change the speed of their rotors relative to the energy needed for lift creation is far too high. In detail:
The moment of inertia of a scaled-up rotor changes with the fifth power of length. The mass of the rotor changes with the cube of the linear scale, and the moment of inertia adds another factor proportional to the square of the linear scale.
A bigger object also needs slower changes, but time scales only with the square root of the linear scale. Next, the engine power available for speed changes will scale with the 3.5th power of scale*.
This still leaves a deficit of one power in the engine power available for speed changes when the helicopter is scaled up.
Lift asymmetries in forward flight can be dealt with by adding a second, counter-rotating rotor, but scaling laws can not be designed out. As Jan Hudec points out, you need to repeat the same trick for forward-backward lift shifting, so four rotors would be the minimum to control this type of helicopter in all directions.

* Proof: Thrust must exceed weight, so thrust goes up with the third power of scale. Rotor disk area scales only with the second power of scale, so a higher acceleration through the rotor disk is required to create more lift per rotor area. If we look at the power required in the static case
$$P_{min} = \frac{\eta_{Prop}}{T_0}\cdot\sqrt{\frac{\frac{4\cdot T_0}{\pi\cdot d^2}\cdot g}{2\cdot\rho}}$$
and insert the scaling factor in all scaleable variables, a power of 3.5 remains for the minimum power $P_{min}$. This is more than the increase in static thrust because the efficiency of the rotors declines with higher disk loading.

And basically assuming it's still a quad-rotor, because single rotor needs cyclic (ok, or auxiliary propellers, but that's not really easier) for control.

Similarly, flies can walk on the ceiling but we cannot.  What works on one scale does not translate to another.

changes with the fifth power of length I'm pretty sure in all my years of engineering college I never once encountered a natural law that included raising to the fifth power. Aerospace is crazy.

A simpler derivation of the 3.5 exponent for power scaling follows: in general, the power required by a heavier-than-air aircraft is proportional to its weight times its speed. The weight scales with the cube of the linear dimension, and the airspeed is squared in the formula for lift, so the power for the proportionality of lift should be 0.5. Since the the power required is proportional to the product of weight and speed, I add the exponents, and the result is 3.5

that can not flap or pitch or adjust otherwise?

Yes, you can design one like that, but you won't get many people to fly it.
In the early days of helicopter flying, any number of crashes occurred before the designers began to account for the problem of differing airflow over the retreating and advancing bladed in forward flight.  If you don't change the pitch angle, the lift changes constantly with the change in airspeed coming over the airfoil.

Without pitch change (called feathering) you will have continually changing lift values rather than a stable "disc" that makes the helicopter controllable.  In the picture above, the blades on the "red" side would have more lift than on the "blue" side, so the helicopter would naturally roll or pitch, with a stronger rolling motion the faster forward you are going.  Flapping is a reaction to the lift increase as the blade advances, and is needed to avoid that same kind of imbalance between advancing and retreating blades.  (Getting that right is some serious engineering, test, and development work).  It also addresses that fact that you don't have a perfect blade track, and thus you will be "flying" each blade into the vortices of the one preceding it.

The helicopter wouldn't roll left but backwards (making it gently slow down) due to gyroscopic precession. Simplified, the advancing/retreating blade problem is a self-stabilizing one. If you accelerate to the point where the imbalance becomes a problem your helicopter will start to resist against acellerating further, until you have reached an equilibrium at the maximum possible speed the craft can fly.

@NilsWerner That isn't what happened to the first tries out of hover towards forward flight ... in a lot of cases they didn't "self correct" but instead crashed .... but I corrected the point on that since gyroscopic precession is indeed a factor.

@KorvinStarmast, The problem is that the gyroscopic effect requires flapping to work. If the body is hanging freely under the rotor, the tilt lags behind the force by all 90°. But if there is a direct torque from the rotor on the body either via offset hinges of an articulated rotor or flexing of a “rigid” one, the lag is lower, typically 70–80°. And those mechanisms still transfer just small fraction of the force and let the blade flap. Before they knew they need to let the blade flap, the lag due to gyroscopic effect was smaller still or the blades simply broke off.

@JanHudec or the blades simply broke off  that rarely ends well, usually it results in fatalities.

@KorvinStarmast, of course. I am just saying that retreating blade producing less lift being self-correcting on modern helicopters is not in contradiction to it causing crashes in early experiments.

Yes, controllability can even be accomplished with only one (rigid) rotor.
Degrees of freedom
In a three-dimensional space there's generally six degrees of freedom (DoF):

forward/backward
left/right
up/down
roll
pitch
yaw

Most aircraft allow engine rpm and velocity to be controlled separately (variable pitch propeller/rotor) as a seventh DoF.

rpm

Multi-engine aircraft can have even more degrees of freedom. In your proposed helicopter design, the pilot can only use main and tail rotor rpm to control seven DoF.
How to control seven DoF with only two levers?
Turns out you can't. At least not independently. We'll have to sacrifice the independence of some of them.
5 DoF
The most obvious thing to drop is the independence of horizontal movement and attitude. To move horizontally, we can just roll/pitch the whole chopper in the desired direction and apply upward power. Most real world helicopters use this configuration.
4 DoF
When we're not constrained by the rotor's tip speed, its moment of inertia or the engine's useful rpm range, we can drop their independence next. This is the case with most electric RC helicopters. Quadcopters, for example, have four control inputs (the four engines' power settings) and thus allow independent control of the four remaining DoF:

up/down
roll
pitch
yaw

Other 4 DoF configurations, like two coaxial rotors plus cyclic pitch and roll, achieve the same level of controllability.
3 DoF
The next thing usually sacrificed is the ability to perform coordinated turns. A lot of fixed wing RC aircraft don't have ailerons and thus allow only skid turns, but are pretty well behaved otherwise and still easy to fly. The same applies to helicopters, so we ditch cyclic roll control.
2 DoF
Things become a bit harder now. We had reduced our helicopter to three control inputs (main rotor rpm, tail rotor rpm, cyclic pitch) and it was still pretty capable and useful. Now we loose something valuable: the ability to contol forward speed. We fix the main rotor at a slightly forward position, so our helicopter moves slowly forward at all times, just like a gyrocopter. We can't hover in place anymore nor fly fast, and we need a runway to take off and land. We still reach our destination though.
1 DoF
Things. Become. Nasty.
When we give up our tail rotor, the helicopter starts turning around itself at high speed. A human pilot will fail to keep it under control, and the passengers won't enjoy it either. It is, however, still possible to move it around in a coordinated manner: every time the helicopter points in the desired direction we momentarily increase power, making it move forward a little faster, and vice versa. Modulating power means the helicopter will violently move up and down, but average power over a full turn still allows us to control its average altitude. As already stated, timing and magnitude of the power variations allow for position corrections.
Such a helicopter has actually been built by the ETH Zürich. Enjoy.

It is indeed possible. One of the first helicopters was the Petróczy-Kármán-Žurovec PKZ 2 Helicopter, fitted with two contrarotating, coaxial rotors that had fixed blades, with no provisions for flapping or pitch change:
https://oldmachinepress.com/2012/09/24/petroczy-karman-zurovec-pkz-2-helicopter/

Theoretically yes, you could build a full-size quadcopter with four fixed pitch rotors, and control it through independent variation of the rpm of each rotor. The power density now achievable in permanent magnet electric motors (eg, 25 hp in a 85mm diameter motor) makes it seem possible to build a small, one man quadcopter with a single motor/generator, but I don't think it would be a very useful machine. The larger and heavier the rotors, the more inertia they have and so the more pronounced the lag in control response that would result in comparison with a conventional helicopter.

Yes and no.
I've never seen such a design for a large helicopter but there are plenty of micro sized RC helicopters which utilize such a scheme using a pair of contra rotating main rotors and a smaller tail rotor to control pitch.

This kind of design works fine, albeit difficult to control for Palm sized toys but does not scale well for larger vehicles.
First off, while the design does offer yaw and pitch control, it does not offer a means of roll control making flight - and in particular hovering - much more difficult.  Second, helicopters are designed with rotor blades that can flex, flap and feather to dampen vibrations and yield a smoother ride with less chances of structural damage from turbulence, mishandling, etc. than a fixed rotor design.
There are also the problems in cruise with lift asymmetry over the rotor disc, the is would create unwanted rolling moments which the design could not cope with, as mentioned above.

The Soviets/Russians have a whole family of helicopters with co-axial rotors, produced by the Kamov design bureau. See Kamov Ka-27, Kamov Ka-31, and Kamov Ka-50 for examples.

Note that even "fixed pitch" RC toy helicopters are not really no-blade-angle-change designs. They use a flybar to automatically change the pitch of the advancing/retreating blades to enable stable flight.

I think it is possible to design such a helicopter with a fixed rotor blade only. Yet it won’t fly very well. And you’ll be facing some difficulties in controlling it. In order to make a more complex helicopter, you’ll need to count a lot of things, the moment of inertia, for instance.

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Please see the Japanese product Gen H-4 which has no pitch control but only speed control - that too differential speeds to take care of yaw. This unique system not only has tail rotor but the tail boom also is absent.

Thinking outside the box:
If you can't effectively brake the rotors could you break the airflow that applies the lift?
Given that the amount of lift is controlled by the air flow I see no reason why it wouldn't be possible to interfere with that using separate structures above and/or below the blades. By raising or lowering this interference you could adjust the amount of lift by increasing/reducing the distance between the interfering structure and the blades themselves. You'd no longer need to tilt the blades themselves, which could improve the structural integrity. The distance of the interfering structures on the right and left could be differentiated to compensate for forward (or reverse) motion.
Unfortunately I have no way to establish whether this could be implemented without risking the blades hitting the interfering structures or whether it could apply enough of a difference to the lift. I'm no engineer, but there would obviously be other risks to at least discount, particularly as I'm unsure whether it would be possible to make the interference continuous, otherwise resulting in stress on the blades as they bend slightly each time they move into/out of the interference, which could also result in vibration build up.

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How many flying hours does one need to become a commercial pilot in the Philippines?
I'm trying to calculate all the expenses to become a pilot in the Philippines.

It's a good idea to narrow your question to one jurisdiction (EU/ US etc.) :)

and on a second note, it's also good to write what type of pilot you're trying to become: commercial or private?

Saw that you edited it to include 'commercial', but it's great if you can add which area/ country of the world you are in- otherwise this is very broad....

...and are you considering being a fixed wing aircraft pilot or a helicopter pilot?

While CAAP seems to be pretty (or even very) vague on the topic, this is what I've been able to find:
To start with the private pilots license:

You must also complete the required minimum of 40 hours of widespread flight training. The hours of flight time consists of at least 20 hours of dual flight instruction, at least 10 hours of solo flight, and 10 hours of which can be solo flights or dual.

Then you will need to build on this to get a commercial pilots license:

You will need about 220 hours of total flight time to get your CPL.

* Another source suggests you need a minimum of 150 hours. Be aware however that this is not an exact science: Even for the PPL it can take 60 hours to 'get the feeling for it', so it is difficult to estimate exactly how much you will need. While I'm not a pilot myself I think it's a good idea to be on the conservative side and overestimate the hours you will need for a PPL and CPL.
Source
This is probably unfortunately what you have also been able to find. It is however a very good idea to go past the flight school in person and talk to them about this topic, since it's uncommon, and they can probably give you a better estimate. Be aware that there can be several more costs that are not visible at first sight (checkrides for instance) that can add to the tally so even the ones that appear the cheapest are not.

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What is the standard for tachometer calibration / Hobb's equivalency?
I've heard that 1 tach hour = 1 Hobb's hour at maximum RPM.  I've also heard that tach equivalency is at "cruise" RPM, although that seems vague.
I believe I've also heard that the accuracy of tachometers is regulated (I think to within 50 RPM).
Because engine time, and often TTSN, is measured by tach hour, there surely must be a strict standard for each aircraft for what RPM the tach counter should be set to.
What is the standard for tachometer calibration? Max RPM? Cruise RPM? Something else?

FWIW, I didn't notice the faa-regulations tag and that means I closed your question immediately. I still think it's probably a dupe but if you disagree please let us know what isn't already answered in the other question and we can re-open.

FAA regulations only have Air Time and Flight Time. We all have a clock or watch so we can accurately record time for the logbook. We are all lazy though, and that is why there is such a reliance on Tach Time or Hobbs Time. I voteted to reopen as this does pertain to FAA Regulations.

FAA Advisory Circular AC 43-9C points out the legalities of using Tach Time or Hobbs Time. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43-9C_CHG_2.pdf

@MikeSowsun: Thanks for the link. I couldn't see anything about how it must be calibrated; did I miss something or do you know of any regulations that specify this?

@Pondlife: I do believe they're different: Where to find... is helpful if you own a plane (the answer is specific to Pipers), my question is more abstract and more helpful if you're looking to buy or rent or are interested academically (if tach calibration is not regulated, why wouldn't everyone set it to redline?). It's possible that the answer to my question is that there is no regulation and tachometer calibration is entirely governed by convention; but if that is the case, I think that fact is interesting enough to have it's own question.

Voting to reopen.  The "dupe" question doesn't provide an answer beyond "at cruise RPM" which the OP already acknowledged.  The question is asking for more definition & depth than that, along with perhaps a source for that "at cruise RPM" specification. Seems like a legit new question, definitely more specifically focused than the other one.

Hobbs time is most useful for tracking log time (and billable time in rentals.)
Tach time is simply a counter of revolutions of the engine, displayed as "hours."  Calibration is basically at normal cruise RPM, which can vary for different engine/prop/desired speed.  The tach counter is approximate at best, but it is what we have.

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What counts towards the 250 hours required for CPL?
FAR 61.129 states that "for a commercial pilot certificate with an airplane category and single-engine class rating must log at least 250 hours of flight time as a pilot that consists of at least:
  (1) 100 hours in powered aircraft, of which 50 hours must be in airplanes.
  (2) 100 hours of pilot-in-command flight time, which includes at least—
      (i) 50 hours in airplanes; and
      (ii) 50 hours in cross-country flight of which at least 10 hours must be in airplanes.
  (3) 20 hours of training on the areas of operation listed in §61.127(b)(1) of this part that includes at least—
      ..."
What counts towards the 250 hours of flight time as a pilot?  Planes? Helicopters? Gliders? Hangliders? Paragliders? Paramotors? Wingsuits? Hot air balloons? Lawn chairs with helium balloons attached to them?
I would think that the skills from flying balloons is not very transferable to planes, so what are people's views on half your hours being from "flying" a balloon, or something similar?  E.g. What do pilot examiners, employers, insurance agents, think?

tl;dr: You can log time iff it has a tail number. No ultralights. No drones.

The regulations on what can be logged for flight time are under 61.51.

Sec. 61.51
Pilot logbooks.
(j) Aircraft requirements for logging flight time. For a person to log flight time, the time must be acquired in an aircraft that is identified as an aircraft under Sec. 61.5(b), and is--
  (1) An aircraft of U.S. registry with either a standard or special airworthiness certificate;

  (2) An aircraft of foreign registry with an airworthiness certificate that is approved by the aviation authority of a foreign country that is a Member State to the Convention on International Civil Aviation Organization;

  (3) A military aircraft under the direct operational control of the U.S. Armed Forces; or

  (4) A public aircraft under the direct operational control of a Federal, State, county, or municipal law enforcement agency, if the flight time was acquired by the pilot while engaged on an official law enforcement flight for a Federal, State, County, or Municipal law enforcement agency.

The list of what qualifies as an aircraft is in section 61.5

Sec. 61.5
Certificates and ratings issued under this part.
(b) The following ratings are placed on a pilot certificate (other than student pilot) when an applicant satisfactorily accomplishes the training and certification requirements for the rating sought:

(1) Aircraft category ratings--

(i) Airplane.
(ii) Rotorcraft.
(iii) Glider.
(iv) Lighter-than-air.
(v) Powered-lift.
(vi) Powered parachute.
(vii) Weight-shift-control aircraft.

(2) Airplane class ratings--

(i) Single-engine land.
(ii) Multiengine land.
(iii) Single-engine sea.
(iv) Multiengine sea.

The following sections indicate what are included under the other categories.
So, piloting a hot air balloon counts toward the flying hours, as long as you're rated for it,  but not the airplane hours. Since ultralights don't have an airworthiness certificate they don't fit under 61.51 (j)(1). Therefore no logging hours in those.
That's the FAA's requirements. Employers and insurance companies can have additional requirements. An example of this is that to qualify under the "open pilot" clause of someone's insurance policy (if they have one) it's pretty common for insurers to require a pilot to have 500 hours of PIC time, 10 of which have to be in the specific model. Depending on the contract, "model" can mean, for example, that time logged in a Cessna 172R doesn't count for the 10 hours required in a 172S.

"So, piloting a hot air balloon or an ultralight counts toward the flying hours" - You can't log flight time in an ultralight, because 61.51(j) requires the aircraft to have "either a standard or special airworthiness certificate", and ultralights cannot have airworthiness certificates. (That's assuming that the ultralight isn't a foreign, military or public aircraft.)

@TannerSwett You are correct. I hadn't thought of that. I'll have to edit.

@TannerSwett And if the ultralight is foreign-registered, located in the foreign country, and has a true airworthiness certificate (from the foreign aviation authority) and is described as an "ultralight" on that certificate, then can you log hours in it (for the purposes of obtaining an FAA rating under part 61?) What if the foreign-registered and foreign-domiciled aircraft is too heavy, too fast and carries too much fuel to be considered by the FAA to be an ultralight, but it says "ultralight" on the true airworthiness certificate anyway? Then can you log hours in it (for the purposes of obt

It's just what the regulation says:  you must log at least 250 hours of flight time and at least 50 of those hours must be PIC time in airplanes and 10 hours of cross country PIC time in airplanes.  As for the other two hundred hours?  They can be in any other kind of aircraft you like.
It's actually a very common way to build raw hours.  A lot of fixed wing pilots get rotorcraft certificates in a fraction of the total time than if they started training from scratch in helicopters.  It also works well with gliders, hot air balloons, you name it.

How about a lawn chair with helium balloons tied to it?

That's an LTA gas balloon by the regs, so yes I guess you could log time in it.

Do aircraft not need to be of some approved model to log time in? o.O

All you need to be is arropriately certificated for that particular category or class or have a type rating for the aircraft in question.

Theoretically if you held a remote pilot certificate you could log your flight time flying a DJI Phantom or similar sUAS. So, should I start logging my part 107 time on my Mavic?

I'd never imagined you could log drone hours.  I'm sure rotorcraft are common, but how about paragliders or balloons?  What would a pilot examiner think about that?  What would employers and insurance agents think?  Are there any advisory circulars or anything else from the FAA that gives guidance on this?

Actually that's not true, if you read the regs.  You can log PIC time even if you are not the sole occupant of the aircraft and no rule states that PIC time cannot be logged in a UAS.  See §107.19.

As an update ymb1 is correct; UAS are not a type of aircraft defined under §61.5.  Therefore per §61.51 you cannot log UAS flight time toward aeronautical experience for a pilot certificate or rating.  So drones are out for this.

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Why would a C150 tachometer bounce so much that the needle fell off?
On a long flight in a C150E, the tachometer started bouncing a little bit and the severity of the bouncing gradually increased until it was extreme: The tachometer was spinning in loops and making a loud screeching sound.
 The counter continues to increment.
Here's a video of the tachometer in the last 10min of our flight. Just after that video, the needle fell off, but the screeching sound persists and the metal pin at the center still seems to be spinning:

What could cause this?
I understand the tach needle is not powered by any gear mechanism, but rather a small alternator that converts the angular velocity of the tachometer cable into a current which exerts a force on the needle.  This should be highly reliable and I don't see how it could cause this behavior.

"a small alternator that converts the angular velocity of the tachometer cable into a current which exerts a force on the needle." is a fancy way of describing two disk in close proximity, one turning, one not. See my explanation in my answer below.

So dd the touch screen function on the tacho stop working also?  What happens if you try a two-finger gesture to drag it back to place?

We ended up having to replace both tachometer and cable.

Cessna 150s have a mechanical tachometer driven by a mechanical tach drive cable geared to the engine.
The tach needle is moved by sensing spinning magnets driven by the tach cable.
They do wear out over time and yours has reached the end of its life.

So you think it's internal to the tach and not a problem with the drive cable? If it wore out, why would it not simply show a lower (or no) RPM? Why would that cause this behavior?

It could be either the cable or the tach.  You will have to get it serviced either way.

"Yours has reached the end of its life."  I'll say.

It appears like you have never disassembled a tachometer, now or as a kid. ;-)
These old type meters consists of two disks near each other. One is driven to rotate by the cable coming in from the engine (or weels, if measuring the speed of a driving vehicle).
The other disk is connected to the needle, and is spring-loaded, so it can't rotate freely.
The rotating disk tries to drag the needle-disk along with it, because of magnesizm and currents induced (the actual details are not important, it could be air or a liquid). What matters is that the amount the needle-disk can turn before the force of the spring is equal to the force from the turning wheel, this force is proportional to the speed of the disk.
The faster the wheel turn, the further the needle goes.
If one of the disks gets bent, or some debris, rust, dirt, bugs gets between the disks, you get the mechanical scratching noise. In this case the needle-disk can start rotating at the same speed as the incoming disk, the spring breaks, and the needle will hit the stop pin from the other side, and will probably break off.
So it is "just" opening it, clean out the debris, and fixing a new spring and put the needle back on.
I don't have a clue if it is cheaper and at all possible to either fix or replace it, giving that a repaired flight instrument have to be certified, I understand.
Also, as the digit drums turned as usual shows, there is nothing wrong with the cable or the drive on the engine.
EDIT: If I imagine the worst case, the inside of the cable could be too long, causing the rotating disk to be pressed inwards, ruining the bearing so the two disks touch each other. Or a sealing might have gone bad in the engine end, causing oil to meander inside the cable into the meter. Or the bearings in the meter have finally worn out after many years of use.

Myself I wouldn't be surprised at all to see 54 year old (from 1965) mechanical tachometer with 5000 hours on it starting to break down from all that age and vibration.
You can get a new TSO compliant replacement unit for as little as 250 bucks...
https://www.aircraftspruce.com/catalog/inpages/mech_tachs.php
...so the broken one in the plane is likely headed for the trash bin.  You'd be nuts to get it overhauled unless you can get someone to do it for that price or less.

Or just leave it. I mean, it's not like you change gears in the air. Hardly critical information anyway :)

Besides not being legal, it is an important instrument because exceeding redline RPM, in theory, overstresses things.  Plus it's your only indication of actual power output.  In the US you just have to show that it works on an annual inspection.  In Canada you have to verify it reads within 4% of true RPM using a strobe each annual.

This exact chain of symptoms happened to me on an automotive speedo - wobble, screech, increaing to extreme wobble, needle falling off, odo still working... exacerbated by low temperature in my case.  This is due to old lubricant not having the correct viscosity due to hardening up from age.  It was like this for many hours.  I put a drop of oil in the right place, and it was fully cured and the repair held for over a year so far. The needle snapped back on, but it took some iterative testing to get it to point correctly.
So I expect your unit should be very repairable.
Of course, being aviation, this work must be done by someone certified.  The crux of the work would be comparable to what I did, but with proper testing and formalities.

Where was the right place for you?

The input shaft, plus some spinning it back and forth and aiming it downward so gravity and motion helped the lubricant descend.   But this wasn't aviation equipment, if mine misread, my worst case scenario was a speeding ticket.

The most likely cause of this problem is a lack of lubrication in the drive shaft for the tachometer.  It might be fixed temporarily by disconnecting the tach drive shaft from the tach head, removing the drive shaft, lubing it, and forcing some oil or grease down the shaft.
Or you could replace the entire drive cable assembly.
Please note that this level of maintenance is not allowed to be done in the United States by the pilot/owner as preventative maintenance by 14 CFR Section 43.  Legally you will need a sign-off by a repairman holding an Airframe and Powerplant license, aka an A&P.

If it is just a problem with the drive cable, is it possible to fix the tachometer, or is there no easy way to reattach the needle?

@Zaz if you clip the needle back on, it will have to be in the right place, and will probably fall off again as the clip/friction fit is already loose.  Glue may help, or it may jamb up the central shaft.    I've done something similar succcessfully in an old car speedo, but regs may not permit that in an aeroplane dashboard.

Would just disconnecting & oiling the cable be allowed without an A&P sign-off? Is it only replacing the cable that needs the sign-off, or both?

@Xen2050, Since this procedure is not listed in 14 CFR 43 the answer is that what you describe is not legally permitted unless you hold an A&P certificate.  Skip Miller

Where in the question is the US mentioned? The applicable regulations might be those of Sri Lanka, Tanzania, Estonia, ...

@Peter Taylor you are correct.  My answer only applies to aircraft under US jurisdiction.  My original post is corrected.

Most C-150's had a Stewart Warner tachometer. They are considered disposable because they  are assembled by crimping the front bezel on to the case.
Also neither an A+P or an IA can work on an instrument. This is a job for a repair station with the correct rating.
If you can find such a repair station, they will laugh at you.
If you buy a high enough quality tach you might be able to get an instrument shop to paint the markings on the face, otherwise you will have to put them on the glass. Not as nice, but either way you must have both the tachometer and the proper markings.


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Why would a C150 tachometer be sluggish?
After having an issue with a tachometer bouncing so much that it fell off, I now have the opposite problem with the replacement (Mitchell D1-112-5025): The tachometer is sluggish. When I open the throttle from 1,000 to 1,700 for the runup, the tachometer takes about 6s to show 1,700 RPM. The delay seems even more pronounced when I reduce power. The smaller the change in RPM, the longer it takes the tachometer to update.
My A&P says that it just needs breaking in, which could possible because the sluggishness has reduced since the tachometer was installed; however, I was under the impression that modern tachometers should work without sluggishness immediately.
The counter increments as expected.
How should I approach this problem? Is it common for tachometers to need >15 hrs to break in? Is it possible for a drive cable to cause this issue (continue to spin, but in such a way that the tach speed is sluggish)? Could some kind of installation issue have caused this problem?
UPDATE Mar-22: Removed the tach cable, inspected outer and inner cable, washed, dried, lubed with graphite, and replaced. Cable seemed good, but the tachometer is still sluggish.
UPDATE Mar-24: Tachometer is now beginning to exhibit the same symptoms as the previous tachometer before the needle spun off; the tach is still sluggish, but the needle is now bouncing considerably.

I remember your last question, it seems to me you may have a problem with the tach cable rather than the instrument itself. The bouncing you had before sounded like the cable was binding, and now you have slow response, which could be another symptom. Did your A&P check that?

@GdD: No. He seemed convinced that it wasn't the drive cable. He seemed to think they are pretty much indestructible.

I think you need a second opinion. That doesn't sound right to me and the statement that instruments need "breaking in" is suspect too. Instruments have to function properly out of the box.

@GdD: We removed the tach cable, and my A&P thought it looked good. Other than the very slight kinks in the outer cable, I thought both looked good too. We cleaned, lubed with graphite and reinstalled. Now it's bouncing as the last one did. You think I just need to get a new cable? My A&P thinks the new tach just happens to be broken also. Is it possible that the gears on the engine are stripped? Is there anything else that could be causing this?

If the gears were stripped then you'd be getting consistent behavior @Zaz, the fact you're getting different results every time you try something new with the tach cable convinces me more that it's the issue. If the cable was fine then lubing it wouldn't change anything. A visual inspection of the outside won't tell you if it's worn inside.

It turned out to be the tachometer cable after all.  After replacing the cable with a new one, the tachometer works as expected.

Good to hear it's solved. I got a JPI EDM900 about a year ago, electronic display, sensor picks up RPM from the magneto  or something, no more spinning cables.  Had a 150 many years, ago, 1994-1996.

@CrossRoads: Thank you. I considered the EDM 900 but didn't want the cost and hassle.

I understand.  Sometimes inexpensive is the way to go.

No you don't have to "break in" flight instruments.
When a TSO'ed instrument is new it will get an Acceptance Test Procedure (a functional test) from the factory done before it is released and it has to perform to specification.  There is no such thing as a break in in service.
That being said, sometimes parts get by the ATP and malfunction in service, so you never know.  In my years in the regional airline industry, "bad from stock" is not uncommon even with super fancy Transport Category components.
Problems with the flex drive could be a factor, but a flex shaft would have to be binding and winding up a hell of a lot to create that kind of lag.  It's still something that could be checked.
Before that though, you should call Mitchell's tech support and describe what it's doing and see what they say.   Maybe they'll tell you there is a break in, but I'd be pretty surprised if they did.

I emailed Mitchell; will probably call tomorrow if there's no response. Is it possible that the gears on the engine are stripped? Is there anything else that could be causing this? My A&P inspected the inner and outer cables and said they are fine - any chance he is wrong?

I would say there's something going on with the instrument internally.  There is a little gearbox inside that drives a signal generator, who's output drives the needle which is pretty much just a voltmeter.  Lag would suggest high friction in a bearing or bushing.  If they tell you that's normal, well in that case I'm stumped...


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How are aircraft controlled that have no forward view out of the cockpit?
Modern aircraft tend to have quite reasonable cockpit visibility. But throughout history there were some that had literally no visibility directly forward.
The best known example is probably Ryan Spirit of St. Louis:

but there were others like Supermarine S6. Granted, they were all special purpose planes. But still, how did the pilot align with the intended runway and ensure the runway is clear? There was no ILS to help him, so it still had to be done visually. And how did he avoid obstacles and other aircraft?

Really silly: Can't conceive how pilot can see and avoid!? - But it (Ryan Spirit of St. Louis) set historical record :-)

@menjaraz either I do not understand your comment, or you have missed the 'no forward visibility' part.

@federico: Indeed, it's about a partial visibility. Maybe I should phrase it:  Can't conceive how pilot can see and avoid properly without appropriate forward visibility!? I think of the case of some low obstacle (e.g trees) in the landing phase.

@Federico Just FYI, URLs are allowed to omit the protocol (in other words, start at the //). That resolves to HTTP when the document containing the link is requested over HTTP, and to HTTPS when the original request is HTTPS. Thus not incurring any HTTPS penalties for those who browse over HTTP, but providing the HTTPS benefits for those who browse over HTTPS.

You don't need a panoramic view to land, and in Lindbergh's time there was no other traffic to avoid. Navigation is easy enough through side windows (in many modern airplanes you can't see the ground out the front unless the nose is pointed down) and you can just yaw the plane left and right for the times you do want to line up with something. Airfields 100 years ago were quite literally fields, so you didn't need to be all that precise about it. Lindbergh had a periscope and was used to flying mail planes with the front seat occupied with the bag, so it wasn't anything new.
Even today, tail draggers have basically zero forward visibility on the ground so they taxi by watching the edge of the pavement with the occasional sharp s-turn to check ahead.

I missed the then low intensity traffic point.

The preferred landing technique for a Pitts (which has essentially zero forward visibility when slow for landing) is to fly downwind/base/final as one big arc.  You're constantly looking out the left side at the runway (assuming left traffic) until on short short final.  At that point you know the runway is clear and if you can't see it, it must be right in front of you.

Landing is no big problem. You memorize landmarks left and right to the intended landing direction and look sideways anyway to get a good idea when to flare. No big deal. Formation flying or a pylon race are quite different, however. There the restricted view will be a big handicap.

@DanPichelman: The same basic technique was used to land the F4U Corsair on a carrier.


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Why do carburetors tend to produce richer mixture at higher altitude?
The pressure drop in the venturi is proportional to air density and the fuel is at ambient pressure in the float chamber, so I would expect the fuel flow to reduce proportionally with density, and that response to preserve the fuel-air ratio over changing altitude.
But in practice that does not seem to be the case. Proper response to altitude requires additional modification that most carburetors don't have, so the pilot usually has to lean out the engine as they climb. What am I missing here?
(Update) More specifically, I would expect that at the same RPM, the volume flow rate will be the same—because the engine pulls in its displacement per revolution. Now velocity in the venturi $v$ is just
$$ v = \frac{\dot V}{A} $$
Where $\dot V$ is the volume flow rate and $A$ is the cross-section of the venturi. So it will also be the same independent of altitude. Since dynamic pressure
$$ p_d = \frac 1 2 \rho v^2 $$
And that is also the pressure that pulls in the fuel (when the float chamber is open to ambient pressure). Substituting mass flow
$$ \dot m = \rho v $$
$$ p_d = \dot m \frac 1 2 v $$
and as long as $v$ is mostly constant,
$$ p_d \sim \dot m $$
This still leaves open the dependence of fuel flow on $p_d$. If the relation is reasonably close to linear, it should mean the venturi mixes properly by mass. I can see a reason why higher pressure should cause less than linear increase in fuel flow, but not much why it should cause more than linear increase in fuel flow—but that is what the actual behaviour would need.
Note: Did you notice the extra $v$ conspicuously missing from the last equation? That suggests the mixture should become richer with throttle opening—which is actually the reason there are extra fuel jets after the throttle that pull in extra fuel when the throttle is at idle and slightly above. It might also explan what is going on here, but would require explaining why the speed should increase when the density is lower.

The fuel could be going through an engine driven fuel pump. Then the fuel might not be at ambient pressure.

@Jan is on right track, fuel orifice is designed to add excess fuel even below sea level.  Fuel lean control valve pinches off fuel flow VOLUME, to maintain proper mixture at all altitudes.  Air density changes with altitude, fuel density does not.  It has to be adjusted.

Possible duplicate question: https://aviation.stackexchange.com/questions/24097/why-do-we-lean-the-mixture-when-the-air-become-less-dense

@MikeSowsun, no, that is not a duplicate. The question asks about what the mixture should be.

Are you asking for cars or airplanes?  The same thing happened to cars before EFI was common.

@KorvinStarmast, I am asking for any engines with a simple carburettor and no electronic controls. Of course the same type of carburettor will have the same effect when used in a car—the only difference is that aircraft usually operate in larger range of altitudes, so the effect is more noticeable.

This is a really good question and it's disappointing that there is not a good answer. I wish people hadn't upvoted any of the current answers, as they are all wrong. None of them address the fundamental first-principles issue being asked.

I figured out the answer and posted it at https://engineering.stackexchange.com/a/52181/27170.

My thought, and I may be wrong, is that there is an incorrect assumption baked into this question.  My sense is that the pressure of the fuel in the carburetor bowl is not ambient but rather is a function of the fuel pressure mechanism--electrical pump, engine driven pump, or gravity--and none of those pressures are in any way influenced by ambient pressure or density.  A Cessna feeds fuel to the engine because gravity is pushing down on the fuel, not because ambient pressure in the tanks are.  I think the underlying premise that a carb bowl is at ambient pressure may be the flaw.

@Max, the carburetor bowl is at ambient pressure—or rather at inlet pressure—because there is a free surface and the space above it is connected to a static port ahead of the venturi (the carburetor needs to feel any ram pressure, and supercharging if present, the engine feels). The fuel nearly stops in the bowl, so how the fuel system injects it there has minimal effect.

The simple reason is that high altitude changes the density of air, but not the density of fuel.
Most simple carburetors use a simple venturi design that mixes air and fuel by VOLUME.
But, the correct air/fuel mixture must be based on MASS, not Volume.
If the air/fuel Volume is correct at sea level, it will be too rich at altitude. This is because a given volume of air will have less Mass at high altitude, while a given volume of fuel will have the same Mass at high altitude.
Aircraft carburetors have a mixture control to "lean" the volume of fuel to the volume of air, and are then able to maintain the correct air/fuel ratio at all altitudes.

But why does it mix by volume? As the same volume of air flows by (if rpm stays the same, it should), it generates less pressure difference (because that is proportional to density) and therefore pulls in less fuel—by both volume and mass, because density of that didn't change. But it pulls less, proportionally by density of the air, therefore mixing properly by mass, not by volume. I understand there is an error in that reasoning, because it does not match the reality—but I am asking where specifically.

It is probably simple physics, but not exactly obvious. In either case, the Venturi effect is simply the kinetic term of Bernoulli's equation, so density and square of velocity, but I don't see a reason for the velocity to be higher (piston engines are constant volume, which suggests it should be the same).

This answer is incorrect. Carburetors are more complex than mixing air and fuel by volume. There is a pressure differential from the float bowl to the venturi and this pushes fuel out the jets. As the plane climbs, the pressure in the float bowl reduces, which means less fuel is ejected per stroke. This in turn means less fuel is ejected per volume of air.

I figured out the answer and posted it at https://engineering.stackexchange.com/a/52181/27170.

It's not pressure that forces fuel into the venturi as much as the vacuum pressure sucking it out. Fuel is pumped or gravity fed to the carb, but then it's metered into the bowl by the float. Fuel sits in the bowl before getting pulled into the jets and then into the venturi. There is air in the bowl, sure, and as that air pressure decreases with altitude there is a bit of a decrease in the pressure behind the fuel, however the part you may be missing is that air can mix with a much higher ratio of fuel than what is ideal for an engine. Airplane engine carbs are generally tuned so at sea level they deliver slightly over the ideal ratio, this is done by restricting the fuel flow. If it wasn't restricted the engine would run rich on the ground.
As density altitude increases the amount of air going through the venturi decreases, but the air still can hold more fuel so the mixture richens even though there's less pressure.

What amount of fuel the air “can” hold is not really relevant. The amount it pulls in is. The amount it pulls in depends on the pressure drop in the venturi. But this pressure drop decreases linearly with the density of that air. So why does the amount of fuel pulled in not decrease the same way?


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How many hours do cabin crews work?
Flight crews are limited to 100 flight hours a month and 1000 flight hours a year, and usually paid by flight hour too. But is it the same for cabin crews or do they have their own rules for monthly hours? Is there an aviation regulation regarding them (they are safety critical crew members after all) with an ICAO recommendation, or are they subject to just work laws of their home country?

Limited by whom? That doesn't sound like a globally valid rule

@J.Hougaard, I don't know by whom it is limited. That's why I am asking. For pilots it is limited by regulation and as far as I can tell all countries follow the same recommendation.

Seems like an FAA-specific rule. See https://www.flightdeckfriend.com/how-many-hours-can-pilots-work-in-one-day/ Please add the USA tag if this question is about the USA


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Who logs Pilot-in-Command time with all automation, autopilot, auto throttle, FMS, Autoland doing the flying?
Who gets to log PIC, if the First Officer programs the FMS and turns on the autopilot at 1000FT AGL while the Captain calls the checklist?

Whoever has designated themselves PIC for that flight, regardless of who is flying the plane. For example I can be PIC and never touch the controls. Usually the Captain is PIC. PIC is more than just doing the flying, they are the one taking responsibility for the flight, its safety, and its outcome.

Which country/regulations are you asking about? And this question is closely related, if you're asking about the US.

@RonBeyer It may not be that simple. At least under US regulations both pilots could be logging PIC, for example.

@Pondlife True, there are situations that both can log PIC, however on most commercial flights (flights with a First Officer, FMS, and AP), I'd say that 99% of the time only one person is PIC, the exception being training flights.

At my company, the senior crew member is always responsible PIC, unless stipulated prior to the flight.  Company policy.  Logging is governed by regulations, but responsibility by company policy and the regs.

@Traveler can you turn on an FSM, climb a B737 to 1000ft, and turn on the autopilot, setup for an autoland, and some stuff you missed: follow all the FAA regulations, react to a single or dual engine flameout over NY, respond to TCAS alerts, and many unthinkable disasters? I can't, so I can accept that I sit in the back and the professional in the front can call themselves the PIC

@Bageletas I don't think its a question of calling themselves PIC at all, but whether the person logging PIC is always the captain, or it is the first officer who programmed the FMS and flipped the switches. There are two professionals up front, usually only one of which is considered PIC. The confusion of the OP is about who gets that designation considering automation is doing most of the work and the FO may be doing the programming.

Already 4 downvotes for what seems a legitimate question... ?!

@Ron Beyer I thought (and I'm guessing the 4  downvoters too) that the question was sarcastically asking "why call anyone PIC if the plane flies itself" so my response was sort if tongue in cheek. If the OP can clarify I'd gladly delete my comment.

you log PIC because you are in command and legally responsible for everything that happens on that flight, not because you were pushing/pulling on some levers and buttons.. geez

@mins and it is only getting worse. This stack has a serious problem. I posted on meta: https://aviation.meta.stackexchange.com/q/3327/1467

The guy at the controls is still flying the plane; the AFCS is only doing what the pilot tells it to do; no autopilot or any other automation flies the airplane.  This is necessary to understand to avoid becoming a smoking hole in the ground and plenty of pilots have killed themselves by running out of fuel, CFIT, etc simply because the autopilot or similar device designed to reduce workload said they could.

In the US, there are two types of "PIC" that can be logged & may be interesting to report -- such as for an interview, perhaps.
Most common when starting out is "sole manipulator of the controls" -- and FAR Part 61 (61.51.e.1.i) defines this.  This includes essentially "sole manipulator of the autopilot," so the pilot who is designated as the PF -- pilot flying -- can log his time as PF as PIC, even though the autopilot is engaged & is driving the controls.  Early on, the time that you've spent "flying the plane" is of interest -- are you proficient and experienced taking off, landing, using the automation, and so forth.  (The standards for logging don't really give a way to distinguish between 10 minutes of hand-flying and an hour on autopilot, vs the whole time being hand-flown. It's not a perfect system.)
Of more interest when interviewing for jobs requiring significantly more experience is PIC as defined in FAR part 1 (1.1, definition of "Pilot in Command"), which amounts to essentially "who signed for the aircraft & is reponsible for the overall flight?"  Airlines who are considering hiring you are interested in this sort of PIC time, because they want to know that somebody has entrusted you with their expensive aircraft for enough hours (typically 1000+) that you've proven to be a good pilot IN COMMAND of not just the controls but the overall flight.
One person I talked to who did airline interviews (as an interviewer), said that when he looked at a logbook and saw every other leg logged as PIC, he knew that this pilot was essentially the copilot, the second-in-command of the flight, flying every other leg, but still responsible to the other pilot, who'd signed for the aircraft & was going to answer for it if things went wrong.  Then at the point when the logbook started showing every leg as PIC, that's when this pilot became the designated PIC, per the FAR Part 1 definition, and every leg was his responsibility, regardless of who was PF and who was PM.  That's the point at which the hours were "interesting" for hiring purposes.
At some point in one's career, the ability to manipulate the controls starts to become a given, and what distinguishes the pilots you want to hire from those you don't becomes factors like judgement or decision making.  Regardless of who is flying the leg, somebody has to be the final authority on decisions like, do we need to upload more gas?  Is this airport acceptable (not just legal, but wise) as an alternate? How long are we willing to hold before we punt on Plan A and divert to the alternate?  All sorts of stuff like that.  And the captain is the final authority on all of that just as much on the First Officer's legs flying as he is on his own legs flying.  (Which isn't to say he doesn't solicit input -- he certainly should -- but the final decision is his.)  Those are the decisions that occur during FAR Part 1 PIC, that may or may not be yours to make during Part 61 PIC.  Thus the different ways to count and report one's flight time.
Related discussion of Part 1 and Part 61 PIC time and logging thereof.


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Why don't airplane piston engines have mufflers?
It is understandable jet engines couldn't have mufflers, but even long before the jet age, airplane piston engines never had mufflers the way cars do.
Is there any specific reason?

I don't have numbers for it but mufflers reduce engine power.

@ymb1 Certainly related, probably not a duplicate; that question asks why are they so noisy (to which the answer, in part, may very well be "because they lack mufflers", as per the top-voted answer there); this asks why no mufflers, to which the answer cannot be "because they lack mufflers" because that would be circular reasoning.

Faulty question.  Most do have mufflers.  Exceptions being very old ones, such as warbirds with radial engines.

They reduce engine power, add weight, have limited life before they burn out, and add new risk factors like fuel leaking onto a hot muffler. Apart from the need to meet noise regulations (which is a political requirement, not a technical one), those are four reasons no good aircraft designer would even consider using them - they totally fail the "simplify and add more lightness" aircraft design principle.

The downvotes are probably because piston engines do have mufflers

Every modern GA aircraft that I am aware of has a muffler. Single engine planes use a muffler shroud to heat air for the defrost and cabin heat. The muffler isn’t nearly as large or effective as the ones on cars but a large part of the noise from an airplane is from the prop, so having a larger muffler would not eliminate the noise.

@alephzero All those objections apply to cars, too. And political requirements are requirements, too. It says so, right in the name.

Aircraft tend to operate further away from the general population than cars. Cars have been also been able to bypass mufflers on the highway since very early days.

When I used to tow gliders up in the air, we had mufflers on the motor planes. As well as 4 bladed lower-noise propellers. And we did run on unleaded Avgas. And we flew special patterns in order to not pass to close to sensitive neighbours. It can be done.

Today, most GA aircraft in Europe do have mufflers so they can pass the ever more stringent noise requirements. Here is one mounted to a Cessna 172 (picture source):

Historically, mufflers were considered as a disadvantage because they reduce engine performance by increasing back pressure. By partially blocking the exhaust flow, the muffler increases cylinder pressure on the last upstroke of the cycle (the exhaust stroke) so it faces more resistance against moving up. Also, more of the burnt gasses remain in the cylinder so less fresh fuel-air mixture can be ingested in the next cycle. At most, in aircraft with an open cockpit a tube was installed to duct the exhaust gasses away from the pilot. Below is a picture of a Mercedes D.IIIa in a Fokker D VII (source):

However, night flying would make aircraft easily detectable by their exhaust flames, so in WW II tubes were added to the exhaust stack in order to avoid optical detection. Below is a picture of an Avro Lancaster with Bristol Hercules engines (source):

Our much better understanding of piston engines now allows to design mufflers which do not cause much power loss and in case of a tuned resonance muffler you even get more power at the design speed because a reflected pressure wave will arrive from the muffler at the exhaust port just when the valves close and will increase cylinder pressure. However, given the low RPM speeds of our old-fashioned aviation piston engines, those mufflers need to be large and the equally old airframe designs have no space for them. So in aviation the mufflers are still causing a power loss.

The most well-known tuned exhaust system is made by Power Flow for general aviation aircraft. http://www.powerflowsystems.com

@Pugz: Just another snake oil vendor …

Fill me in please!

@Pugz: From their FAQ: 'We have accomplished flight-testing and found that drag caused by the tailpipe is overcome by thrust coming out of it.' Yes, their exhaust seems to be better, but being larger, it causes more drag. This supports what I said in the answer above.

lol that’s pretty funny. Thanks!

Even in the US planes designed in the 40s and 50s, the most common planes have mufflers.
Mooney's do.
And the ever popular Cessna 172

The direct answer to the question you asked is that there's usually much more separation between an operating aircraft and almost anybody else who might hear it, so noise simply doesn't matter nearly as much as it does with something like a car that frequently operates within, say, a meter of other cars and pedestrians, and often only a few tens of meters from houses, offices, hospitals, etc.
On the other hand, I do feel obliged to point out that contrary to popular belief, an exhaust system can reduce noise levels without causing loss of power--in fact, a properly designed system can actually increase power in many cases, especially some that are quite applicable to most aircraft.
Just for example, a simple tuned expansion chamber typically looks roughly like two cones with their large ends welded together. It helps increase power output fairly simply.
When the engine's exhaust value opens, exhaust starts to flow out of the exhaust port (being pushed fairly quickly by the piston). That means we a have a stream of fairly dense exhaust moving away from the exhaust port at fairly high speed.
When the exhaust port closes, that exhaust gas keeps moving away from the port, leaving a partial vacuum behind it.
In an "open pipe" exhaust system, atmospheric air flows into fill the vacuum very quickly, so by the time the exhaust port opens again, the exhaust gas has to "push" the air out of the way to flow out of the port.
With a tuned exhaust system, we have a pipe (of some sort) near the exhaust port to keep air from the atmosphere from just filling the vacuum next to the port. The dual cone expansion chamber does more than that though: it's designed so the dense exhaust gas bounces off the far end of the chamber, and back toward the port. It gets back to the port end of the chamber, and bounces off it again so it's now moving away from the exhaust port.
What we're shooting for is that the partial vacuum behind the dense exhaust gas is just outside the engine's exhaust port just as the exhaust valve opens. When this happens, that partial vacuum is actually helping to "suck" the next "pack" of exhaust gas out of the combustion chamber.
As to this helping reduce noise: the noise from the exhaust is basically because of the "packs" of compressed exhaust gas followed by rarified air immediately following. With the tuned chamber, we're letting the next pack of compressed exhaust "fill" in that partial vacuum. As a result, the gas flowing out of the exhaust has a much more consistent pressure.
As to why this is particularly applicable to aircraft: mostly because in an aircraft the engine's speed is much more predictable most of the time. Unlike something like a car, most aircraft are basically designed around a cruising speed, and spend the vast majority of their time operating within a fairly narrow range of engine RPM, so it's fairly easy to design an expansion chamber for that speed, with minimal consideration for other speeds.

What you describe sounds like a basic muffer used on two-cycle racing bikes and some high performance chainsaws: 2-cycle muffler.  I can see the "two cones put together " shape.

@JPhi1618: Yes, that's one common application of this design. It's not restricted to two-stroke engines (though for a four-stroke engine, the time between valve openings roughly doubles, so the chamber has to be ~twice as long for the same RPM).

"there's usually much more separation between an operating aircraft and almost anybody else who might hear it, so noise simply doesn't matter nearly as much as it does with something like a car". My parents live about a mile from an airport. Piston-engined planes flying hundreds of feet above their house make much more noise than cars driving down the street.

@DavidRicherby: Much of that noise is caused by the propeller.

@PeterKämpf OK, but the answer claims that noise from planes doesn't matter much because planes are far away. I'm pointing out that this argument doesn't hold much water. That part of the argument doesn't depend on what part of the plane is making the noise.

@DavidRicherby: not mattering as much is quite a bit different from claiming that it doesn't matter at all. You're saying that it's loud from hundreds of feet away--and I agree. My point was that it simply wouldn't be accepted at all if aircraft were even within tens of feet like cars often are to houses and pedestrians.

That's a valveless 2-stroke expansion exhaust you're describing. A 4-stroke high performance exhaust is an expanding cone only. All aircraft piston engines are 4-stroke. "Partial vacuum" does not make sense to me.

@Koyovis: Really?

@JerryCoffin Ah ultralights are aircraft too, indeed.

@JerryCoffin There is even a company, Power Flow Systems, that makes retrofit exhaust systems for 4 cylinder Lycoming engines that increases horsepower by intelligently managing intake and exhaust. They claim it also reduced cabin noise, but that may be because it redirects the exhaust rather than having a quieter muffler.

Propellers often run at a high enough RPM that the tips of the blades exceed the speed of sound.
Ever notice that a prop-plane is extremely loud at take off, but very quiet on landing?
Supersonic blade tips made mini sonic-booms.
Our ear hears an 'angry snarl' sound.  Not the engine, not all the time.
This is why a 5-bladed prop is somewhat quieter than a two bladed prop, each running with the same net thrust.
The two bladed prop needs higher RPM, this pushes the tips past the sound barrier.
A 5-bladed prop runs at lower RPM, less sonic booms.
OK, the point is this: If your propeller is capable of making noise that greatly exceeds engine noise, why silence the engine?
Yes, a prop-plane at straight and level flight is not as quiet as a car, but the thing is literally miles away from the nearest unprotected ear, so less need for sound suppression of the engine.
Here in Seattle, where it seems everyone has a sea-plane, regulations over blade-count are coming into effect.
2 blades?  Nope, too much noise at take-off.
3?  OK, better. Still loud at high RPM's.
5 or 7?  Yay!  Never need to spin it fast enough for supersonic operation.
Some newer props have many oddly curved blades, and run very quietly.
Quiet propeller = efficient propeller.

For a prop plane to be "literally miles away from the nearest unprotected ear" it has to be at an altitude of at least 12,000ft over any area with any kind of population density. (I.e., pretty much the whole of a place like England.)

I dispute the claim that propellers are often run with supersonic tips.  Specific models of aircraft have been noteworthy for doing so, but it is not common.

Some quick back-of-the-envelope calculation shows that supersonic tips are at least plausible. The speed of sound is around 300 m/s, or 18000 m/minute. The speed of the tip depends on the diameter of the prop, and the speed it rotates. If the prop rotates at 2400 RPM, 18000 m/s translates to 7.5 m/revolution. So a prop at 2400 RPM would go supersonic if the radius (= length of a blade) is around 2.4 meters (or around 8 feet). Of course, smaller props will go supersonic when they rotate faster.

@KevinKeane And how many planes have 16ft-diameter props? Nobody disputes that there are some planes with supersonic prop tips (e.g, the Tu-95 "Bear" which, btw, has 18ft props) but, as Erin says, that's not the norm.

Re "...iterally miles away from the nearest unprotected ear...": You must have some awfully long extensions on your shoes to allow your feet to reach the rudder pedals :-)  I suspect the real reason is the same as why many motorcycles, snowmobiles, and the like don't have effective mufflers, and some people replace their car's (semi)-effective muffler with a louder one: the noise, and the annoyance it causes other people, gives them a feeling of power.

Plane engines are designed to run close to WOT (wide open throttle) in a narrow range RPM for most of the flight.
Matching the pipe length to the RPM is called exhaust tuning, which improves the performance and to my understanding reduces the noise.
This means tuning the exhaust of each cylinder should be simple, basically cut to the right length and left open would be best.

(Source) Example exhaust tuning.


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How are the IFE Server, Floor Disconnect Box (FDB), Seat Electronic Box (SEB) and Seat Display Unit (SDU) connected to each other?
I tried to understand the data protocols used to connect InFlight-Entertainment (IFE) Server, Seat Electronic Unit (SEB), Floor Disconnect Box (FDB) and Seat Display Unit (SDU), but I'm a bit struggling about this.
Generally speaking I've seen that the most used transmission protocols for avionics are ARINC 429 (629 in case of Boeing 777) and ARINC 664 or AFDX, since part of the IMA infrastructure, and in other rare case ethernet connections, however I haven't found particular specifications about this particular connections.
Does anybody know something about this or have good sources from which start back my research?

@Gerry can you tell me, at least with the companies you have mentioned before, which protocols/standards you have found there?

I don't know the streaming protocols used. It's been almost 10 years since I had any contact with them. The system was basically a server with Ethernet distribution. Since airline seat configurations change, you need some flexibility in connections. Think of the FDB as a router/connection point for nearby seats, the SEB as a media client (PC, XBOX, etc.) and the SDU is just a monitor.

Is there a specific aircraft you are focusing on? That might help narrow down what IFE system(s) might be used. ARINC 429 isn't a good fit for IFE.

@selectstriker2 I'm not focused in a specific aircraft but instead in a specific IFE brand, Panasonic.

I have not worked with IFEs, just certified avionics, but I suspect that most IFEs uses a centralized server, running some consumer OS such as Windows or Linux. They would then just use an Ethernet protocol such as TCP/IP to communicate. Related to your question: https://aviation.stackexchange.com/questions/15604/how-does-the-in-flight-entertainment-system-works

@selectstriker2 It could be possible indeed but actually ethernet protocols doesn't ensure any kind unidirectionality pretections, if I understood correctly from avionics litterature ARINC protocols are also used for security reasons. In a recent search I found out something about ARINC 628 protocol (part 2 and 3) used specifically for IFE communications in Boeing.
Still I ask myself if is it possible to have other ARINC protocols used to connect IFE components like FDB, SEB, SDU together and in case which ones. About the link I had already read it before writing the question.

@Gerry Thx for your experience feedback, I'll check more information based on this.

This might be a useful resource as far as what ARINC (the organization) is working on for IFE http://www.aviation-ia.com/aeec/projects/cabin_systems/index.html. Not that any of that has to be used for any IFE. It is also important to note that not all ARINC standards are data protocols. ARINC 429 is in no means secure, but it is simple to implement into certified avionics.

@selectstriker2 So is it possible to not have at all ARINC protocols inside IFE and having just an ARINC protocol that connects IFE to the CIDS or the CMS?

It is technically possible to have no ARINC defined protocols in use, as nothing regulatory mandates their use. ARINC 429 is a common avionics data bus because it has mainstream adoption all over the aircraft. IFE isn't safety critical and isn't held to the same stringent software development guidelines (DO-178), or could simply be identified as DO-178C DAL E, which has no safety impact and can just use company design standards. The goal of IFE vendors is to design it as cheaply and quickly as possible to keep up with the consumer media tech as @Gerry stated.

@selectstriker2 Ok but as it was shown but some notable security experts, from IFE is still possible to bring damage to the aircraft services, even though not to the critical ones. This is why I'm looking for information about the current IFE ecosystem, to understand better which is the impact of an attack brought from the IFE.

I assume you are referencing this (or similar) articles: http://www.eweek.com/security/security-vulnerabilities-found-in-airline-entertainment-systems. It is important to note that the IFE system does not interface with the flight systems in any way, so short of turning of the cabin lighting or suddenly getting all of the speakers to play some noise, I'm not sure what damage compromising the IFE system a hacker would hope to cause.

@selectstriker2 Actually you cannot do nothing that interfere with Aircraft Control Domain and even Airline Information Services Domain, but from what I've understood some features like lighting management, audio, EVAC signal and even maybe oxygen maks are deployed in CIDS, that is nearly connected to IFE from what I've found, so you can create a fake "attack" to cause panic to the passengers. Am I wrong? Plz in case tell me if I did wrong assumptions somewhere :)

Airbus IFE system

All data sources and servers are concentrated in the IFE Center which delivers them to the cabin LAN using Ethernet. The LAN itself is Ethernet.
Some data are received by the IFE Center from the Cabin Intercommunication Data System which is itself connected to AFDX (Ethernet, ARINC 664) ADCN network.
The cabin network then distributes data and power to overhead displays and seat IFE units.
Schematic:

Source, page 15
Architecture:

Source, page 15

IFE System for the A350

The IFEC rack is the source for all data sent to the passengers IFE units and the flight attendants panels. It contains files and media servers, is linked to external cameras (ETACS), landscape cameras and SATCOM.

IFE: In Flight Entertainment
IFEC: In Flight Entertainment Center. A system with redundant sources and redundant outputs.
ETACS: External and Taxiing Aid Camera System
SATCOM: Satellite Communications

The IFEC is also interfaced with the CIDS which supply it with data from systems like CDAU and ADIRS and other aircraft systems using AFDX, engine data from PCS, or discrete signals like cabin systems (oxygen) or public address.

CIDS: Cabin Intercommunication Data System, the main way for attendants to control the cabin systems other than IFE.
CDAU: Centralized Data Acquisition Unit
ADIRS: Air Data/Inertial Reference System
AFDX: Avionics Full Duplex Switched Ethernet (ARINC 664)
ADCN: Avionics Data Communication Network
PCS: Propulsion Control system

IFE power is supplied by some SPDB.

SPDB: Secondary Power Distribution Box

The IFEC and SPDB are controlled by ICPs, FAPs, CWSs and RCCs.

ICP: Integrated Control Panel (in cockpit)
FAP: Flight Attendant Panel
CWS: Cabin Work Station
RCC: Remote Control Center

The IFEC delivers data (audio, video, other data) as Ethernet frames to FDBs using a switch. There are actually two or more IFEC switches, each one feeds some FBDs.
FBDs also receive power from the SPDB. Ethernet frames and power are distributed by FDBs to overhead displays and IFE units.

FDB: Floor Disconnect Box. Used as a switch to create the network. FDB ensure network redundancy: Each FDB receives data from one IFEC switch, but as FDB share the same network, IFEC is still available when one of its switch is failed.

Each seat gets its IFE unit which is connected using a SEB. The IFE unit encompasses the SDU, the PCU and headset.

SEB: Seat Electronic Box. A network interface card, with power management.
SDU: Seat Display Unit (touch screen in front of the passenger)
PCU: Passenger Control Unit (interface)

The big picture:

Source

Security aspects

Your question was motivated by the security aspects of the cabin network vs. the other aircraft domains (e.g. avionics or cabin systems).
For Airbus, the cabin IFE network is only a layer 2 LAN with multiple Ethernet segments linked by Ethernet switches. There is no possibility to route malicious packets to other domains, since there is no routable (layer 3) protocol.
The interconnection between IFE and other systems is made through the CIDS, which is based on a redundant "director" which controls data destination. Without other elements, the assumption is security is primarily at CIDS level.
More information in this presentation (some pages are in German, most are in English).


text:
How is that there is no leak through the fuel vents during aerobatics maneuvers?
Can anyone tell me how aircraft such as jet fighters and stunt planes design the fuel tank vent system to prevent fuel leaking through the vents when performing aerobatics, 360 flips and complex maneuvers?
Surely jet fighters don't just let it leak out?

@jjack -- the tank vents allow air to come into the tank to replace the fuel that's pulled out by the fuel pump.

Vents are also used to remove fuel vapours and prevent the fuel tank from pressurising in cars the vent typically runs to a charcoal canister to reclaim fuel.

@jjack because otherwise the vacuum that developed in the tank would suck the fuel back into the tank with more force than the fuel pump sucked it out, the pump would stop pumping, and the engine would stop engineing. And yes, your car has a venting system too.

@PeteBecker: That sounds dangerous - wouldn't it be better to fill the empty space from a bottle of nitrogen or something that won't potentially make the fuel tank explode?

There are 3 common solutions,
1) do nothing, unless the airplane is flown for an extended period of time inverted, there will be no appreciable vacuum created from fuel use and the vent is so small that there will not be appreciable fuel loss.
2) point the vent into the slipstream giving a ram air effect.
3) use two vent tubes (can be mounted either top & bottom or same side), at least one extends to opposite side of the tank.

This picture is for RC or drone aircraft but the same principle is used for full scale aircraft.


text:
What is the maximum allowed intensity for light beams pointing at the sky for non-aviation purposes?
In Hong Kong, I'm designing a show with light beams and i'm thinking using Robe Megapointe lights (https://www.robe.cz/megapointe/). I've been ask by the client to follow the aviation regulation. Though the aviation regulation doesn't give any figure, only subjective indications, and I have no idea if my lights are acceptable or too strong.
The website of Robe announces: 2.200.000 lx @ 5 m and 137.500 lx @ 20 m. I'm trying to find similar regulation references in other countries to make up my mind.
Any of you have seen any figures in that domain?

I retagged the question to [tag:regulations], since the FAA is the aviation authority in the USA, not Hong Kong. Feel free to roll back if you specifically wish to know the FAA regulations only.

Article 80(1) of the Air Navigation (Hong Kong) Order 1995 stipulates that

A person shall not exhibit in Hong Kong any light which —
(a) by reason of its glare is liable to endanger aircraft taking off from or landing at an aerodrome; or
(b) by reason of its liability to be mistaken for an aeronautical ground light is liable to endanger aircraft.
Any such contravention is liable on summary conviction to a fine.

The full text of the regulation can be read here.
Given this text, if your show is going to be anywhere near the approach or departure path to/from the airport (anywhere on Lantau Island, or east/west of the Gold Coast) you should probably refrain from using such lighting. I would strongly suggest you get approval from the authorities well before the event using an experienced local consultant, and prepare for that approval to be given or denied based on subjective analysis.


text:
Why does the A350-900 call out to retard at 20 feet above the runway?
I watched this video of a delivery of an A350.

at 14:50 there is the sequence I'm interested in: the ground radar normally counts down the distance to the ground, but shortly after the 20 feet mark, it calls the typical "retard" to pull the levers back.
Why is it like this and not like normally at 0 feet?

What do you mean by "normally"? And do you mean the callout or the reduction of the thrust?

I am offended that you refer to the pilot as a typical retard.

Why is it like this and not like normally at 0 feet?

Normally is not 0 feet: all Airbus (maybe with the exception of the A380, that might have a longer flare) have a "Retard" call at 20ft, not at 0ft. From the A320 Flight Crew Training Manual:

As a reminder, the ”RETARD” aural alert will sound. In flare, this aural alert will occur at 20 ft, except in the case of autoland, where it occurs at 10 ft.

Where is the answer to the question - WHY? This statement only re-enforces what the original question stated - that the Airbus flight computer calls out to retard the throttles at 20ft.

@jwzumwalt NO. The question "why is this aircraft different?" is based on the false premise that this is the only Airbus doing it, while others have it at 0. the answer is: the premise is wrong, all do it at 20.

I'm no expert on this aircraft but I think it's because jet engines don't respond instantly to throttle changes because combustion is a continuous process, rather than a series of individual strokes in a piston engine.
If you just suddenly reduced the fuel input, you reduce the pressure in the combustion chamber and the flame might go out. Instead you have to do it gradually and wait for the turbine to reduce speed.
These days, the throttle just tells the engine controller what power setting the pilot would like to have, and the engine controller reduces the fuel flow at a rate that the engine can handle.
So (again, at a guess) 20 feet is how long it takes the engine to reduce power.

It depends on the airframe, but in this case, I guess Airbus test pilots determined that 20 ft AGL was the best place to retard the throttles to expedite the roundout with enough energy left to do it safely.
As a general rule, commercial and business jet aircraft are aerodynamically pretty slippery and do not slow up quickly when the thrust levers are pulled to idle.  This fact is compounded when the a/c is in ground effect, which is why jets are generally flown onto the runway as opposed to flow to a stall prior to touchdown.  I would guess aircraft with newer generations of high bypass engines slow up faster that low-mid bypass turbofans and turbojet powered airplanes do.  Some business aircraft, for example the Embraer Phenom 300, suggest the thrust levers should be pulled to idle as the aircraft passes over the threshold markers (piano keys) prior to touching down some 750-1500 feet thereafter (by ATPL standards).

A lot of guessing going on here.  The reason the auto thrust calls for the reduction is simply a reminder to the pilot that it is engaged. It has nothing to do with any of the reasons sited above. These thrust levers are stationary and do not move during flight once the automatic function is engaged, hence the reminder.

IIRC, the callout also sounds with A/THR off.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.


text:
Can an aircraft fly without wings and stabilizers?
Can there be an aircraft (not an airplane like in this other question) without wings and stabs (rudders and elevators)?

Very briefly...

Welcome to aviation.SE! I don't really understand your question, do you have a picture or some reference that will show us what you're asking? This question might help.

Unless you consider fan blades to be wings: https://en.wikipedia.org/wiki/Lunar_Landing_Research_Vehicle

This might be relevant too.

@fooot Aircraft are a superset of airplanes, so the question is not a duplicate.

Helicopters?  Do you consider the rotor(s) to be wings?  If so, why not the turbine blades in jet engines?

There are lots of aircraft that fly without wings and control surfaces.

source

Sure can.  Balloons do it all the time.  For a heavier than air aircraft, there a a couple of options.
Lifting body using a reaction system for stability and control.  Here the fuselage itself creates the lifting force and the aircraft would use a flight computer to control the craft and maneuver it using a reaction control system.  This can consist of thrust vectoring from the engines or separate thrusters, similar to those found on a spacecraft to control roll, pitch and yaw motion.
Another option is a pure powered lift arrangement ie a rocket belt or similar craft which can direct its lift engines to hold it aloft and to propel it forward.

No, aircraft do not need wings or stabilizers. However, they are very desirable for takeoff and landings.

 This is an example of an unmanned aircraft without wings or stabilizer. It could just as easily be manned.
 This is another example of a manned aircraft without wings.

I didn't downvote, but those little fins are stabilizers...

The second rocket you posted (Saturn V) actually has stabilization fins at the bottom of the first stage. But there are rockets which stabilize their trajectory with vernier thrusters and engine gimbal only.

Rocket doesn't really fit the definition of aircraft.


text:
What happens to the neutral point of a fighter jet during supersonic flight?
I understand that for a fighter aircraft, it would have to be inherently unstable. To do this I believe that the neutral point needs to be aft of the cg. I was told that during supersonic flight this relationship might be different. What would change in supersonic flight?

Would the answers to this question be of any help to answer this one? I feel we can mark your question as a duplicate - if you disagree, please edit your question and point out why it is not a dupe.

Yes I agree, thank you for the link appreciate it!


text:
Did turbofan engine explosions become more frequent in last years in commercial aviation?
There are many incidents with turbofan engine failures during last years. I can list:

2010-11-04 - Qantas_Flight_32
2015-09-08 - British Airways Flight 2276
2016-05-27 - Korean Air Flight 2708
2016-06-27 - Singapore Airlines Flight 368
2016-10-28 - American Airlines Flight 383
2017-09-30 - Air France 66
2018-04-17 - Southwest Airlines Flight 1380

This list is not exhaustive.
Question: did turbofan incidents indeed become more frequent in recent years?
If yes, is there a reason of this suggested?

Welcome to aviation.stackexchange!

May depend on the time period of interest and what you count as an incident, but in general over the time span of decades, turbo fan engines are significantly more reliable now than they were previously. You only have to count the engines to see this trend. Many years ago all jets had 4 engines, then 3, and now virtually all new planes have only 2. The reason of this is the increasing reliability of engines. Decades ago planes had 4 engines because the possibility of 2 engines failing during a single flight, while uncommon, was not unheard of. Now days, planes have only 2 engines because reliability of engines is very good. Failure of 2 engines during the same flight is very very rare (maybe not zero, but very rare)


text:
Did Wolfgang Langewiesche ever change his mind about rudder pedals?
I get the feeling that if aviation was a religion and had a holy book, that book would be Stick and Rudder.  Mostly because it's often spoken of with great authority by people who have never read it.
Well, I'm reading it right now.  And let me tell you, Wolfgang has got some opinions.  Here's one of them, from Chapter 11.

The important thing to understand about the rudder pedals is that they are unnecessary; like your wisdom teeth, they serve no very good purpose but can cause much trouble.  The airplane needs no rudder pedals.  It should have no rudder pedals.  In all probability it will have no rudder pedals 10 years hence.

I have to give him credit: he put his money where his mouth was.

However, the fact that it's now 2014 and rudder pedals are still very much in vogue makes me wonder:  Did Wolfgang Langewiesche ever change his mind about rudder pedals, or did he go to his grave defiant to the end?

Very, very interesting. I had forgotten that part of the book. Though auto coordination is pretty cool, and with the age of technology we now have I am surprised there are still rudder pedals

as @flyingfisch mentions, auto coordination is getting better, but there is one thing for which the pedals will always have to be there: de-crab.

@Federico and directional control close to/in a stall, and directional control on the ground, and taxiing/takeoff roll with a crosswind, and, and, and... :)

FWIW, the Ercoupe was designed by Fred Weick, not Langewiesche. :)

@falstro And during an engine failure in a multi-engine aircraft....

@Lnafziger; with today's age of technology and auto coordination, engines never fail ;)

This sounds like an opinion from the ivory tower. I guess he never made a crosswind landing, or he would not have entertained such thoughts.

I have flown the Ercoupe, as shown in the picture but w/o the GPS (it was back in the 1960s). Crosswind landings were crazy. Supposedly stall-proof so no need for recovery? Ha ha. Any aircraft with adverse yaw from aileron deflection will need a rudder to stay in trim. WL is out there on that one.

FWIW, RC planes can now automatically de-crab and fly in straight for crosswind landings without a user-controlled rudder by using active flight stabilization software. However, at least for RC, the rudder is still fun for doing aerobatics. If you never need to do aerobatics I can see how you can remove rudder controls completely with modern software (though obviously not the rudder itself)

As @MDS wrote (but the answer will be deleted): This is not same saying "no need for rudder pedals", and "no need for rudder". If I may ask, as I don't know the book... it would be interesting to explain what the author was suggesting to replace rudder (or rudder pedals) where other see the rudder as required (e.g. crosswind landings).

@PeterKämpf to be fair, back in 1944, there wasn't really such thing as a crosswind landing. You either landed on an open field and landed into the wind, or the airfield had 3+ runways and your crosswind could therefore never be more than 30 degrees off  your heading, making decrabbing rare. Worst case, you'd just land at the airfield 5 minutes up the road, because this was WW2 and there was an airfield every 7th house.

@falstro Correction: Engines never fail, except when you've got a CFI or FE in the right-hand seat.

Try flying a glider without rudder... :P Is the author actually "meaning what he did write" or it is an exaggeration with the purpose of saying "no rudder is still better that wrong rudder", something that may be true...

NO
There is no written record that I have found in researching this question that Langweische ever 'recanted' his beliefs. I cannot source or cite this negative however. I don't actually like this question, since only an answer that he did recant can be sourceable. Any cites showing him supporting his own written beliefs could be disputed by saying "but what about later in life?" This means that a negative answer can only be opinion.
It's not like he left in his LW&T the statement that everything he had written previously was a lie.

That is how chapter 11 of the book begins. IMHO,  I suspect it was a rhetorical statement. For he then spends the rest of the chapter explaining what rudders are used for in aircraft and he contrasts this by giving an example, as a thought exercise, of how it could be done without a rudder.  One needs to read the whole chapter and the context the writer comes from rather than just use a sentence in isolation. Having said all this, the author is entitled to his opinion and to have that critically examined, which he does anyway.

Then why the statement: "It should have no rudder pedals. In all probability it will have no rudder pedals 10 years hence."  It really seems like he thought the rudder should be removed.

I think you gentlemen have missed the point.  Ercoupe aicraft have no rudder pedals at all. The flight controls are designed to keep the aircraft in coordinated flight automatically, thus eliminating the need for the pilot to use the rudder. Since it is possible to build and fly airplanes without rudder pedals Wolfgang is correct. His main objective in pointing this out to the pilot is to emphasize that in the air the rudder does NOT cause the aircraft to turn.
Wolfgang also points out legitimate uses of rudder pedals if the airplane has them, or more precisely, MUST have them because of design inadequacies that leave the designer no choice but to make rudder pedals available to the pilot to address undesirable flight characteristics in certain modes of flight. But again, in the air the rudder does NOT cause the aircraft to turn.
Wolfgang did not need to recant his position on rudder pedals because he was correct. He did miss that the trend towards building automatically coordinated flight controls would be short lived. No doubt in 1944 he believed the Ercoupe was the start of things to come. This is understandable considering that no man can predict the future.

I think you mean to refer to the Ercoupe, not the Aerocoupe.

Strictly-speaking, an aircraft can be turned using just the rudder.  It's not normally best practice to do so, though.

I don't think he every changed his mind because the statement, and the enclosing chapter, is a proof by contradiction. Assume the contradiction ("Planes don't need rudders!") then go on to show why they do, and therefore the assumption must be false.


text:
Would the Aeroflot Flight 1492 have been able to dump its fuel first before landing?
In the recent Aeroflot Superjet 100 crash, it seems to me that (at least) the landing gear was spiked upwards, penetrating the fuel tanks, which might be one of the factors that lead to disaster.
In my naive mind, dumping the fuel before landing might have mitigated this factor.
Would it have been possible for this airplane to dump its fuel before landing?

Lack of time, lack of control and it was over a populated area???

It may not have that capability...

DaveGremlin that's why I included Russia tag. I remember a Jumbo of Olympic Airways dumping fuel, but my home is close to the sea. @RonBeyer I didn't think of that. It would be really helpful if someone could say more on this..

I'm voting to close this question as off-topic because it asks for speculation about a recent accident, which is explicitly off-topic here.

No it's not off topic because the fact is that it didn't dump its fuel, because it can't, so this isn't speculation.

@JohnK that fact doesn't make it on-topic. Speculation as to why it wasn't dumped does.

Juan what? The sentence regarding the organs was a question, not a speculation. In any case, that was edited away already, so I hope now it's on topic.

No it wasn't dumped because it CAN'T.  That's not speculation.

Voting to reopen because it is a question about the reason for, and ability to, dumping fuel.

The fact that the aircraft crashed is not speculation, it is a fact.

This aircraft does not have fuel dumping capability. In general, only large wide body airliners have fuel dumping capability.
Aircraft can land overweight quite easily but getting stopped on the runway safely is the main problem.
Even with fuel dumping, aircraft will often still plan to land overweight. The amount of fuel to be dumped would be planned to make a safe landing on the available runway without excessively heating the brakes and tires.

Correct, and they won't dump any more fuel than they need to in order to bring the landing within margins.  Fuel is money, and it's also much worse for the environment than exhaust, and unlike exhaust, impacts the local environment (a matter of interest to local ATC).  That is to say, CO2 from exhaust is quickly dissipated by wind, but dumped fuel falls down into the local environment, affecting local smog.

In most cases an overweight landing is no big deal if it's a "normal" landing.  The only fallout is that a special inspection is required after the fact to look for structural damage, which should be fine unless the landing was hard.

@Harper : "fuel is money" - if they only cared about money, even then it would make them lose much more money to have the plane end up in a big fireball with most of the passengers dead. Also, they don't have to dump fuel before every landing, just before emergency landings, which are usually on the one in a million scale. So for such rare occasions money and environmental factors shouldn't be an issue.

They probably didn't need too - in smaller aircraft like the SSJ100, the Max Landing Weight (MLW) is close to the Max Takeoff Weight (MTOW). It's unlikely that it was departing Moscow at MTOW, so that would be my reasoning - they may well have been below MLW. This is just speculation though, so don't take my word for it - wait for the accident report to come out to be certain.
https://www.superjetinternational.com/wp-content/uploads/SSJ100_Datasheet.pdf

Harry thank you for your answer, however Mike's answer seems more concrete.

Yep, I definitely agree!